Machine type communication (MTC) User Equipment (hereinafter referred to as MTC UE), also known as Machine to Machine (M2M) user communication device, is the main application form at this stage of Internet of things. Low power consumption and low cost are important guarantees for its large scale of applications. Currently, the M2M devices deployed in the market are mainly based on the Global System of Mobile communication (GSM) system. In recent years, due to the increase of the spectrum efficiency of Long Term Evolution (LTE)/LTE-advanced (LTE-A), more and more mobile operators choose the LTE/LTE-A as the evolution direction of the future broadband wireless communication system. The LTE/LTE-A based M2M multiple types of data services will also be more attractive. Only when the cost of the LTE-M2M device is lower than the MTC terminal in the GSM system, the M2M services can be really transferred from the GSM to the LTE system.
Currently, main alternative methods for reducing the cost of the MTC user terminal include: reducing the number of receiving antennas of the terminal, reducing baseband processing bandwidth of the terminal, reducing the peak rate supported by the terminal, and using the half-duplex mode. However, the cost reduction means the performance degradation, while the LTE/LTE-A system cell coverage requirement cannot be reduced, therefore some measures should be taken in order to achieve the coverage performance requirements of existing LTE terminals when using MTC terminals with low-cost configuration. In addition, the MTC terminals may be located in locations such as basement and corner, the environment where it is located is worse than that of the general LTE UE. To compensate for the decreased coverage caused by the penetration loss, parts of MTC UEs need more performance improvements, therefore, for this scenario, the uplink and downlink coverage improvement of parts of MTC UEs is necessary. How to ensure the user's access quality is the first issue to be considered, and it is necessary to perform an improvement design for the Physical Random Access Channel (PRACH) in the LTE/LTE-A system to ensure that the MTC UE can normally access to the system.
The position information of physical resource blocks (PRBs) occupied by the random access response message (RAR) in the LTE/LTE-A system is included in the downlink control information (DCI) and sent through the physical downlink control channel (PDCCH). Furthermore, the abovementioned DCI information further includes a 16-bit Cyclic Redundancy Check (CRC for short), and the abovementioned CRC further uses a 16-bit random access radio network temporary identity (RA-RNTI) to be scrambled, and the scrambling method is:ck=(bk+ak)mod 2 k=0,1, . . . ,15
Wherein bk is the (k+1)th bit in the CRC; ak is the (k+1)th bit in the RA-RNTI; ck is the (k+1)th bit generated after the scrambling.
The UE receives the RAR message and obtains the uplink time synchronization and uplink resources. However, at this time, the UE cannot determine that the RAR message is sent to itself rather than another UE, because there is possibility that different UEs send the same random access sequence on the same time-frequency resources, and they will receive the same RAR through the same RA-RNTI. Furthermore, the UE also does not know whether there are other UEs using the same resources to access randomly. To this end, the UE needs to use the subsequent Msg3 and Msg4 messages to resolve such random access contention.
The Msg3 is the first message transmitted in the PUSCH based on the uplink scheduling and by using the HARQ (Hybrid Automatic Repeat request) mechanism. In the initial random access process, what is be sent in the Msg3 is the RRC layer connection request message (RRCConnectionRequest). If different UEs receive the same RAR message, they will obtain the same uplink resources and send the Msg3 message at the same time, and in order to distinguish different UEs, a specific UE ID will be carried in the MSG3 to distinguish different UEs. In the case of initial access, the ID may be the UE S-TMSI (if existing) or a randomly generated value of 40 bits.
After sending the MSg3 message, the UE will immediately start a contention elimination timer (the timer should be restarted at each subsequent Msg3 retransmission), and the UE needs to monitor the ContentionResolution message (Msg4 message) returned by the eNodeB to itself during this time.
Within the time configured by the contention elimination timer, the UE receives the Msg4 message returned by the eNodeB, and the UE ID carried therein matches with the one reported to the eNodeB in the Msg3, then the UE thinks that it wins in this random access contention and the random access is successful, and sets a temporary C-RNTI obtained in the RAR message as its own C-RNTI. Otherwise, the UE believes that this access fails, and restarts the random access retransmission process.
Because an improvement design is performed on the Physical Random Access Channel (referred to as PRACH) in the LTE/LTE-A system to ensure that the MTC UE can normally access to the system, an improvement design also needs to be performed on the Msg2, the Msg3 and the Msg4 in the LTE/LTE-A system to ensure that the MTC UE can normally access to the system.